In modern motor vehicles, electrical machines, such as synchronous motors, are increasingly used as drive motors. In order to regulate the electrical machine, rotation angle sensors are frequently arranged on the electrical machine in electric or hybrid vehicles, said rotation angle sensors sensing the speed and the rotation angle of the rotor and of the electrical machine. Such a rotation angle sensor is known from DE 102 10 372 A1, for example.
By way of example, a rotation angle sensor may have a sensor element and a sensor disk, the sensor disk having a signal trace with a known shape. If the signal trace is sinusoidal, for example, then the rotation angle sensor delivers a sinusoidal signal. Usually, a rotation angle sensor with a sinusoidal signal trace has a further sensor element that is fitted at an interval of 90° with respect to the first sensor element and therefore delivers a cosine-shaped signal. For these two signals, i.e. the sine signal and the cosine signal, it is possible to calculate the rotation angle using the arctangent. The rotation angle of the rotor of the electrical machine may be needed particularly for field-oriented regulation of the electrical machine.
For safety reasons, the correct operation of the electrical machine needs to be monitored constantly. By way of example, EP 1 479 157 B1 discloses a method for fault detection for electric motors in the motor vehicle domain.